An emulsion is a mixture of two immiscible liquids, where one liquid is dispersed in the form of small drops in another liquid that forms a continuous phase. Most conventional methods for making emulsions involve drop breakup using shear or impact stresses generated by manual or mechanical agitation. However, such stresses are not uniform across the system, nor are they finely controlled. Emulsions formed in these ways thus consist of drops that are highly polydisperse in size (Shah et al., Materials Today, 2008, 11, 18-27). Microfluidic devices offer an alternate and versatile route to produce emulsions.
Water and oil emulsions have been found to be useful in numerous molecular biology techniques. For example, enzymatically catalyzed amplification of single nucleic acid molecules in emulsion droplets have found use in DNA sequencing and the generation of libraries of compounds for screening. Such water in oil emulsions been generated by microfluidic systems and by bulk emulsification by agitating the water and oil mixture. Such bulk emulsification has been performed in a filtration apparatus and by use of test tube vortexers, e.g., VWR® multi-tube vortexer. Examples of systems for generating emulsions for use in molecular biology processes can be found in US 2013/0164789 A1, US 2013/0164789 A1, and WO 2010/117461 A2. Such techniques have been inefficient and hard to replicate for the reliable production of droplets suitable for molecular biology techniques such as DNA amplification by PCR. The inventors have created new techniques and instruments for reliably making aqueous in oil emulsions of various droplet sizes with high efficiency and high uniformity of droplet size.